Week 2 of development Flashcards
The trophoblast differentiates into ____________ (1)and _____________(2).
The embryoblast differentiates into the ___________ (3) and ___________.(4)
- Cytotrophoblast
- Synctiotrophoblast
- Epiblast
- Hypoblast
When is the bilaminar disc formed?
When the blastocyst implants
Day 8
Describe the cytotrophoblast
It is the inner layer
It forms mononuclear cells that migrate into the synctiotrophoblast.
Describe the synctiotrophoblast
It is the outer layer
-It is a multinuclear mass that is expanding rapidly, and as an irregular shape
-Unable to clearly view cell boundaries
Endometrial cells undergo ___________ to facilitate implantation
apoptosis
What regulates trophoblast fusion?
Cyclic Adenosine Monophosphate AMP (cyclic AMP) pathway
What happens to the connective tissue surrounding the implantation site?
Connective tissue surrounding implantation site begins to
degenerate adjacent to the synctiotrophoblast.
How does the blastocyst get nutrition?
The synctiotrophoblast engulfs the endometrial cells that died due to apoptosis. That is how it nourishes itself
What are lacunae?
Irregular spaces in the synctiotrophoblast which fuse. The fused spaces are called lacunae.
What is the function of the lacunae in the synctiotrophoblast?
The trophoblastic lacunae fuse to form an intercommunicating network which communicates with maternal capillaries (sinusoids) as the synctiotrophoblast penetrates the endometrium further.
Name the usual implantation site
Superior part of the body of the uterus
- More often on the posterior wall than the anterior wall.
Define ectopic pregnancy
Implantation outside the uterus
State the 4 sites of ectopic pregnancy
Tubal (most common) – in the uterine tubes
▪ Ovarian (least common) – at the ovary
▪ Abdominal – in the mesentry of the abdomen
▪ Cervical – sometimes included as uterine pregnancy but is considered ectopic
What hormone does a pregnancy test detect? and what structure releases this hormone?
*HCG (Human chorionic gonadotrophin) produced by synctiotrophoblast enters
maternal blood in lacunae and is the basis of pregnancy tests
Describe what placenta previa is.
Placenta previa is when the placenta partially or completely covers the opening of the cervix.
-It is caused by the implantation of the blastocyst on the inferior part of the uterus.
-This may cause bleeding due to the premature separation of the placenta during pregnancy or at the time of delivery.
What hormones are in the morning after pill?
progestins/anti-progestins - they affect implantation
How can intrauterine devices disturb implantation?
-They can cause a local inflammatory reaction to disturb implantation
- in some cases the device contains slow releasing
progesterone to disrupt endometrial development.
When is the bilaminar disc formed?
Approximately day 8
Describe the two layers of the bilaminar disc
A distinct external layer of columnar cells – EPIBLAST
▪ Adjacent to the amniotic cavity
- An internal layer of cuboidal cells – HYPOBLAST
▪ Adjacent to the blastocyst cavity.
How is the dorsal-ventral axis of the blastocyst defined?
Hypoblast - ventral
Epiblast - dorsal
Describe amnion and amniotic cavity formation
Implantation progresses – fluid-filled space appears in
embryoblast
- Space is the primordium for Amniotic Cavity
* Amnioblasts separate from epiblast forming AMNION
which encloses Amniotic Cavity
_____________ forms floor of the amniotic cavity, and continues peripherally with amnion
Epiblast
When does the formation of amniotic cavity occur?
Around day 8 - it forms together with the bilaminar disc.
What forms the roof of the exocoelomic membrane?
Hypoblast
What is the derivative of amnion?
Epiblast cells
What lines the primary umbilical vesicle?
-Superiorly there is hypoblast layer.
-Inferiorly there is exocoelomic membrane.
What forms the extraembryonic mesoderm?
Outer layer of cells of primary umbilical vesicle forms
EXTRAEMBRYONIC MESODERM which surrounds
primary umbilical vesicle and amnion
How is the extraembryonic coelom formed?
-The extraembryonic mesoderm increases while changes in the trophoblast and endometrium occur.
-Extra embryonic coelomic spaces now form in the extraembryonic mesoderm
-Spaces fuse to form a large isolated extraembryonic coelom.
How is the extraembryonic coelom formed?
-The extraembryonic mesoderm increases while changes in the trophoblast and endometrium occur.
-Extra embryonic coelomic spaces now form in the extraembryonic mesoderm
-Spaces fuse to form a large isolated extraembryonic coelom.
what is the primordium for the chorionic cavity?
Extraembryonic coelom
The primary umbilical vesicle eventually decreases in size. What causes this reduction?
Extraembryonic coelom formation causes primary umbilical
vesicle to decrease in size.
smaller SECONDARY UMBILICAL VESICLE forms
What forms the secondary umbilical vesicle?
The cells of the hypoblast in the primary umbilical vesicle migrate as extraembryonic endodermal cells to form the secondary umbilical vesicle
During formation of the 2ndary vesicle a large part of the ______________ is pinched off and leaves a remnant.
primary
vesicle
Extraembryonic coelom splits the extraembryonic mesoderm into…? (2)
- Extraembryonic SOMATIC Mesoderm which Lines trophoblast and covers the amnion
2.Extraembryonic SPLANCHNIC Mesoderm which Lines the umbilical vesicle
What structures form the chorion?
The extraembryonic somatic mesoderm and both layers of the trophoblast.
Name the structures that are suspended in the chorionic sac
Embryo
Amniotic sac
Umbilical vesicle
Describe the primary chorionic villi
These villi are vascular processes of the chorion and form
columns with syncytial coverings.
- Once these cellular extensions grow into the
synctiotrophoblast they are termed primary chorionic villi
When is the primary chorionic villi formed?
By the end of week 2
How does the embryo get nutrition
The fluid in the lacunar spaces (embryotroph) passes to
the embryonic disc via diffusion – thus providing
nutrition to the embryo.
How is the primordial uteroplacental circulation established?
The communication between the eroded endometrial
capillaries and the lacunae of the synctiotrophoblast thus
establishes the
PRIMORDIAL UTEROPLACENTAL CIRCULATION
What carries oxygenated blood to the embryo?
Oxygenated blood – via Spiral Endometrial Arteries
What carries deoxygenated blood away from the embryo?
Deoxygenated blood – via Endometrial veins
When do the lacunae in the synctiotrophoblast fuse to form lacunae network?
~ Day 12: the adjacent lacunae have fused to form a
lacunar network
Endometrial capillaries become___________________ to form maternal sinusoids.
Congested and dilated
what is lacunar network primordial for
intervillous spaces of placenta
Epiblast
Columnar cells
Adjacent to amniotic cavity
Hypoblast
Cuboidal cells
Adjacent to blastocyst cavity
What is the lacunar network primordial to
Around which day?
Intervillous spaces of placenta
12
What allows maternal blood to flow freely to the lacunar network
Synctiotrophoblast erodes sinusoids
Since the chorionic cavity is formed by extraembryonic coelom, what forms the chorion?
SOMATIC mesoderm
Where is the Embryo, amniotic sac and umbilical vesicle suspended to?
Chorionic sac
What suspends them to the chorionic sac?
Connecting stalk
What has to be seen at the end of he second week?
Primary chorionic villi
